1. Field of the Invention
The present invention relates generally to a semiconductor device equipped with a transfer circuit receiving an external input data signal and providing a retimed signal thereof as an external output data signal in order to make a cascade connection of a plurality of semiconductor devices, more particularly to a data driver IC to be mounted on a flat-panel display device.
2. Description of the Related Art
FIG. 11 is a block diagram showing a schematic configuration of a conventional data driver 20 that is connected to the data lines of an LCD panel 10.
The data driver 20 includes a plurality of data driver ICs 21 to 24 having the same structure that are mounted on a printed board and commonly connected to lines for providing clock signals CLK and data signals DATA. Therefore, lines parallel to the longitudinal direction of the data driver 20 and lines perpendicular thereto must be formed on the printed board, and the printed board has two wiring layers. In practical, because there is a need to form other signal lines and power supply lines on the printed board, it has six wiring layers, increasing the cost of the printed board.
FIG. 12 is a schematic block diagram showing a data driver 20A that employs a cascade connection in order to overcome such a problem.
In this data driver 20A, each of data driver ICs 21A to 24A is provided with input and output terminals for the data signals DATA and the clock signal CLK, and the input and output terminals are connected through a buffer circuit within the data driver IC 21A. According to this configuration including such a signal transfer section in each IC, cascade connections of the data driver ICs 21A to 24A are made with respect to the data signals DATA and the clock signal CLK, so that there is no intersection between the lines on the printed board, and the printed board has only one wiring layer. In practical, because other signal lines and power supply lines are additionally provided, it has two wiring layers. This allows reducing the cost of the printed board. When such a signal transfer section is formed in each data driver IC, although the cost partially increases due to the increase of chip area, the total cost of the data driver ICs and the printed board can be reduced.
However, since the distance between adjacent lines inside the chip is much smaller than that on the printed board, crosstalk noise between signal lines becomes not negligible. Particularly, in a case where the data driver 20A is connected to a high resolution LCD panel, because the frequency of data signals DATA is relatively high, the crosstalk effect increases. In addition, because an external signal line L1 is longer than an internal signal line L3, their signals have different propagation delay times due to difference of line capacity. Due to the cascade connection between the data driver ICs 21A to 24A, the delay time differences are accumulated, making the timing adjustment difficult.
To resolve these problems, JP 2001-202052-A discloses a semiconductor device comprising a signal transfer circuit which decomposes inputted external input data signals to reduce the frequency thereof, transfers the decomposed signals, combines them to compose the retimed signals of the external input data signals, and outputs the retimed signals.
However, since the transfer direction is fixed, according to whether the semiconductor devices as data driver ICs are disposed along one side or the opposite side of a flat display panel, two kinds of semiconductor devices are required.
If bidirectional transfer circuit is incorporated into the semiconductor device, the wiring area of the signal transfer circuit increases because of the decomposition.